Remote operation of integrated optical modulators for sensor applications or antenna remoting requires a definite polarization input to the guided-wave device. The stability of the state of polarization of the light is important in determining system performance, because many integrated optic devices exhibit a strong polarization sensitivity, and thus require a certain input state of polarization to operate at maximum efficiency. This problem has been dealt with by the use of polarization maintaining fiber, polarization control devices, or by the use of a depolarized source. In the latter case, the laser source is followed by ordinary (i.e. less expensive non-polarization maintaining) fiber and a polarizer which selects the state of polarization from the depolarized signal which the remote device needs for operation. For example, Kersey et al. have proposed phase modulating an optical signal having TE and TM modes, with a time varying modulation signal of about 100 kHz, the result of which was to differentially phase shift the TE and TM modes, effectively scrambling the signal's polarization and producing a de facto depolarized signal. See, Single-Mode Fiber Pseudo-Depolarizer, SPIE vol. 838, Fiber Optic and Laser Sensors V, p. 360.
Additionally, such remote operation must also avoid stimulated Brillouin scattering, which can occur when a long fiber is used with a high-power, narrow-linewidth, source. Brillouin scattering is a three-wave interaction process, in which the optical pump wave creates an acoustic wave in the fiber, which in turn scatters the pump wave into a third wave which travels backwards towards the pump. For significant stimulated Brillouin scattering to occur, the laser field must build up a strong coherent wave within the dephasing time of the acoustic signal, V.sub.b.sup.-1. But if optical phase reversals occur more frequently than spontaneous acoustic dephasing, then the acoustic wave is unable to build up to a large amplitude, and stimulated Brillouin scattering gain is smaller. See, D. Cotter, Suppression of Stimulated Brillouin Scattering During Transmission of High-Power Narrowband Laser Light in Monomode Fibre, Electronics Letters, 18, 638 (No. 15, Jul. 22, 1982). Cotter's paper reports reduction in Brillouin scattering when two signals having closely separated frequencies are launched into a optical fiber. The signals beat together to induce phase reversals which reduced simulated Brillouin scattering.